This invention relates to a railway car bogie and more specifically to an axle box support device on a railway car bogie. Such a device permits the railway car easier passage on tightly curving tracks and good stability for highspeed running on straight tracks.
Although there is a clear need for railway carriages which are capable of increased running speeds and smooth turning on curved tracks and sufficient running stability on straight tracks, running on curved tracks and running stability are mutually exclusive properties, and it is difficult to achieve both objectives. FIG. 7 of the accompanying drawings illustrates schematically a bogie spring system, and FIG. 8 is one example of a dynamics model based on FIG. 7 for a simulation used to evaluate running stability. As can be seen in FIG. 8, there are two factors related to the support rigidity of axles 32 with respect to running stability; rotational rigidity K.sub..phi. around the vertical axes of the axles 32 and lateral rigidity K.sub.1. By optimizing the coefficients of these two factors, running stability can be ensured. It should be noted that 31 indicates the wheels, 33 the bogie frame, and B the railway car body. Focusing on this point, there have been many proposals intended to achieve the dual objectives of running stability and passage on curved tracks. One example is the railway car bogie described in Japanese Provisional Patent Publication No. 58-128958, a plan view of which is shown in FIG. 9 and a detailed view of the axle box support device of which is shown in FIG. 10. The objective of that proposal is to couple bearing boxes 35 having swingable bearings 34 provided at the center of the axles 32 to the bogie frame 33 via a link mechanism comprised of struts 36, 37 and 38 in order to transmit the longitudinal and lateral forces acting upon the axles 32 to the bogie frame 33 via the link mechanism, thus making it possible to reduce the support rigidity of the axle box support device in the longitudinal and lateral directions, which would ensure both running stability and passage on curved tracks. In FIG. 10, 39 indicates another bearing, 40 the axle boxes, 41 the axle springs, 42 the cushioning rubbers and 43 the axle spring seats.
In addition, Japanese Provisional Patent Publication No. 59-106361 is one example of a proposal for suppressing the increase of the moment around the vertical axes of the axles during passage on curved tracks, and the construction is shown in FIGS. 11 and 12. In both drawings the objective is to sufficiently relax the lateral rigidity of the axle springs 44. In FIG. 11, either rubber vibration insulators 46 attached at the mounting location of displacement-proportion type oil dampers 45 or an appropriate rigidity of the mounting location are used to provide elasticity in the longitudinal direction for the axle box support devices. In FIG. 12, a resistance device is comprised by sandwiching the friction plates 48 of friction dampers 47 between rubber vibration insulators 49, and the elastic force in the shear direction of those rubber vibration insulators 49 is used as the stabilizing force in the longitudinal direction for the axle box support devices. When the set resistance force of the resistance device is exceeded, the oil dampers 45 or the friction dampers 47 are displaced, thus suppressing the resistance force with respect to the displacement of the vertical rotation of the axles. 50 indicates the wheels, 51 the carriage frame, 52 the axle boxes, and 53 axle box guards provided with openings .delta. in front of and behind the axle boxes 52.
From FIGS. 7 and 8, the primary factors affecting running stability are, as mentioned above, the rotational rigidity K.sub..phi. around the vertical axes of the axles and the lateral rigidity K.sub.1. The K.sub..phi. value is expressed as 2b.sup.2 K.sub.2 and is determined by the values of K.sub.2 and b. If this dynamics model is applied to the embodiment of Japanese Provisional Patent Publication No. 58-128958 mentioned above for evaluation of running stability, because it is not possible to ensure running stability unless K.sub.2, which is the lateral rigidity of the axle springs 41 shown in FIG. 10, is set to the appropriate value, regardless of the bearings 34 and link mechanisms 36 through 38 shown in FIG. 9, K.sub.2 cannot be set to a very low value. For this reason, when it is necessary to achieve a large angular displacement around the vertical axes of the axles 32, such as when passing over especially tightly curving tracks, the moment around the vertical axes needed to steer the axles 32 increases, and the creep force between the wheels 31 and the rails needed to generate this moment also increases. Thus, either the rate of slippage between the wheel tread surfaces and the rails increases, which would result in faster wear of both surfaces, or steering will not be possible to the necessary angular displacement around the vertical axes, the wheels 31 will have an attack angle with respect to the rails, and the lateral pressure will increase, thus promoting wear of the wheels and the rails and causing a screeching noise. In FIG. 8, K.sub..theta. (=2c.sup.2 K.sub.3) indicates the rotational rigidity existing between the railway car body B and the bogie frame 33.
On the other hand, in Japanese Provisional Patent Publication No. 59-106361, while the railway car is running, in addition to forces acting on the wheels in the direction of movement as a result of power running and braking, if a unilateral type of surface brake is used, an even greater amount of force will be applied in the longitudinal direction. For this reason, if this longitudinal force is applied when the longitudinal support rigidity is kept low by the axle springs 44 shown in FIGS. 11 and 12, this longitudinal force cannot be borne by the axle springs 44, and must be borne by the resistance device, thus resulting in displacement of the resistance device. As a result, because the wheels 50 displace in the longitudinal direction in an approximately parallel state until the axle boxes 52 and the axle box guards 53 contact each other, in addition to the desired cushioning effect in the longitudinal direction being lost, when a curve is entered and the axles undergo angular displacement around the vertical axes, because one of the axle boxes 52 becomes virtually incapable of movement, there is a tendency for the angular displacement around the vertical axes of the axles to be adversely affected. Furthermore, if the lateral rigidity of the axle springs 44 is set to a coefficient sufficiently high to cope with the above-mentioned load in the longitudinal direction, when passing over tightly curving tracks, that rigidity will cause the moment around the vertical axes of the axle to increase, and thus result in a problem similar to that of Japanese Provisional Patent Publication No. 58-128958. In addition, for railway cars which have large differences in the load between the loaded and empty states, because it is necessary to set the resistance force of this resistance device taking into consideration the large load, when the car is empty, a larger than necessary resistance moment around the vertical axes of the axle will be generated during running, which is undesirable.